1. Field of the Invention
The present invention relates to an exposure apparatus,-and more particularly, to a projection exposure apparatus used in manufacture of semiconductor devices (integrated circuit (IC), large-scale integration (LSI) circuits, or the like), image pick-up devices (CCD or the like), liquid crystal display devices, thin layer magnetic heads, or the like.
2. Discussion of the Related Art
In recent years, following advances in higher integration of semiconductor devices, finer mask patterning is increasingly becoming a necessity in a projection exposure apparatus. To cope with such high resolution, focusing accuracy in the image of the mask pattern formed via the projection optical system needs to be improved. In other words, it is necessary to position the exposure surface of the photosensitive circuit board within the depth of focus for the image formation surface of the projection optical system. Variety of methods have been proposed to meet this requirement. For example, by installing a sensor that measures the vertical position of a substrate stage (photosensitive substance) relative to the projection optical system, the exposure surface of the photosensitive substrate is matched with the focused image plane using the origin of the signal from the detection sensor as a reference. In this case, the focal point of the mask pattern image using a fiducial plate surface placed on the substrate stage is measured, and the origin of the signal from the sensor is set to this focusing point.
In the method described above, the origin in the sensor may deviate from the actual focal point of the projection optical system due to fluctuation in environment of the exposure unit, type of mask used, or fluctuation in the imaging characteristics of the projection optical system over time. Therefore, it is necessary to reset the origin of the sensor to calibrate the sensor every once in a while at regular intervals. An example of such calibration of the sensor is disclosed in Japanese Laid-Open Publication No. 05-160003. In this reference, light emitted from a mark on a fiducial plate on the substrate stage passes through a projection optical system, and is reflected at the mask surface. The reflected light returns to the fiducial plate, and is measured when it is received at the light-emitting portion. Then, the focusing condition of the fiducial plate substrate is derived based on the received light quantity.
In the method described above, the illumination system for alignment focal position measurement is different from that for exposure, i.e, focus measurement is carried out under different conditions from that for exposure, which may lead to measurement errors. Also, there is a limit in reducing manufacturing tolerance to the width of the mark on the fiducial plate. Therefore, it is almost impossible to perform the focus measurement using the minimum line width for the mask. (This is because the projection optical system for exposure is typically a reduction type. Thus, the manufacturing tolerance of the mask pattern is much larger than that of the fiducial mask pattern.) Therefore, when an L/S (line and space mark) formed on the fiducial plate is used as the mark, focusing errors may occur due to the difference between the minimum line width of an L/S mark on the mask and the minimum line width of the L/S mark on the fiducial board.
Referring to FIG. 25, the operation of a conventional exposure apparatus is explained. FIG. 25 is a schematic diagram of the conventional projection exposure apparatus.
When shutter 904 is opened by a shutter drive unit 902, light emitted from an illumination light source 900 progresses in the direction A in the figure and impinges on a mirror 906. The light deflected from the mirror 906 enters an illumination optical system 908 and is tuned to yield a uniform illumination field suitable for exposure. Then, the tuned light illuminates a reticle 910. The light, which passes through reticle 910, enters a projection lens 912 and is incident on a predetermined area of a wafer 916 on a wafer stage 914. This way, the image of the pattern formed on reticle 910 is projected and transferred onto the wafer 916.
In general, the above-mentioned projection exposure of the reticle pattern onto the wafer is repeatedly performed for multiple patterns. After processes of etching and film deposition, etc., ICs, LSIs, etc. are formed on the wafer. During such processes, the pattern that was projected onto the wafer in the previous process needs to be superimposed (aligned) with a reticle pattern for the next layer.
To perform such alignment, it is necessary to obtain a relationship between a coordinate system fixed on the reticle and a coordinates system fixed on the wafer. In this example above, the correspondence is obtained using a fiducial plate 918 placed on the wafer stage 914. A wafer alignment mark 920 formed on the fiducial plate 918 and a reticle mark 922 formed on the reticle 910 are observed at the same time to determine the positional relationship.
In more detail, when the shutter drive unit 902 closes the shutter 904, light reflected from a metal surface of the shutter 904 progresses in the direction B in the figure and enters a split mirror 926 of an alignment optical system 924. Then, the light reflected by the split mirror 926 illuminates the reticle mark 922, passes through the projection lens 912, and illuminates the fiducial mark 920 as shown in the figure. This light, carrying information of the alignment marks, is reflected by the fiducial plate 918 and goes back along its incoming path, and enters the split mirror 926. again. Then, the light that passes through the split mirror 926 reaches a two-dimensional image sensor 928 to image the marks 920 and 922 on the image sensor 928. The image of each alignment mark captured by the image sensor 928 is input into an image processor 930, and are analyzed to derive the relative positional difference between the reticle 910 and the wafer stage 914. Such positional difference need be taken into account when moving the wafer stage 914 to align the existing pattern on the wafer 916 with the pattern of the reticle 910 being projected is conducted.
As mentioned above, in the exposure apparatus, the illumination condition of the exposure optical system and that of the alignment optical system are not necessarily consistent with each other. To exposure finer patterns (finer line width), which is becoming popular in recent years, various improvement have been introduced in an exposure apparatus: reducing the wavelength xcex of illumination light, increasing the numerical aperture NA of the projection lens, using a modified illumination technique, etc. With respect to the illumination wavelength xcex, the illumination condition of the exposure optical system and that of the alignment optical system can be made equivalent by relaying light from a single light source by a separate optical system. However, to achieve other methods such as increasing numerical aperture, it is necessary to build a large, complicated alignment illumination system, which is, however, not practical. Therefore, it is difficult to obtain the same illumination conditions between exposure and alignment.
To overcome such difficulties, a method of receiving the actual exposure light in a slit sensor located on the wafer stage has been developed. Although it is possible to match the illumination conditions between exposure and alignment with this technique, this method has a disadvantage in that it is not applicable to a high speed alignment operation using an RA (reticle alignment) image processing system, which is disclosed in Japanese Laid-Open publication No. 05-21314. Furthermore, when signals are obtained by integrating the amount of light passing through a light using slit measurement, this method is not suitable for measuring the width of the L/S (line and space) mark near maximum resolution.
Some of the problems discussed above and additional problems in the conventional art will be described in more detail below. Manufacture of semiconductor devices and the like employs a projection exposure apparatus (e.g. a stepper) in which a reticle (mask) pattern is transferred via a projection optical system onto each shot region on a wafer (or a glass plate and the like) coated with photoresist. For example, semiconductor devices are fabricated by overlaying a plurality of circuit patterns on a wafer in a predetermined positional relationship. When superimposing a circuit pattern on the existing pattern on the wafer, highly accurate alignment between the reticle pattern to be exposed and the existing circuit pattern in each shot region is required.
Such an alignment is disclosed for example in Japanese Laid-Open Publication No. 07-176468. In this alignment method, first, the positional deviation of an alignment mark on the wafer from a fiducial mark on a fiducial mark plate fixed to a wafer stage is detected through an alignment sensor on the reticle side. Then, the reticle is aligned with the wafer stage. In this method, a so-called stage emitting technique is used. In this technique, the fiducial mark for reticle alignment is illuminated by an illumination light having the same wavelength as that of the exposing light from the bottom of the fiducial mark plate to transmit the light from the fiducial mark. The alignment system at the reticle side then detects this illumination light that passes through the alignment mark on the reticle to derive the position of the reticle relative to the wafer stage.
Next, calibration of an off-axis wafer alignment sensor is conducted. The off-axis wafer alignment sensor is installed in the exposure apparatus for detecting a wafer alignment mark (wafer mark) on the wafer to align the wafer with the reticle. First, the position of another fiducial mark on the fiducial mark plate is detected by the off-axis wafer alignment sensor. Then a positional relationship between the detection center of the off-axis wafer alignment sensor (the center of the measurement field of the sensor) and the center of the projected image of the reticle pattern (exposure center) is derived. This step is called a baseline check, and a length between the detection center and the exposure center is called a baseline length. The thus detected baseline length is stored in the exposure apparatus and used in aligning the center of each shot region with the exposure center with high accuracy.
In general, the wafer stage coordinate system in a projection exposure apparatus is measured by mobile mirrors fixed to the wafer stage and external laser interferometers. Any changes in the positional relationship between the mobile mirror and the fiducial mark plate affect the baseline length, generating alignment errors. These changes may occur due to thermal deformation or the like caused by heat from exposing light during exposure. For this reason, the fiducial mark plate and the mobile mirror were arranged close to each other on the wafer stage and it was believed that the change in this positional relationship was negligible. Based on this belief, during wafer replacement operation, for example, the reticle alignment and the baseline check have been performed quickly and almost simultaneously using the fiducial marks on the fiducial mark plate without drastically moving the wafer stage.
As described above, in a conventional projection exposure apparatus, the reticle alignment, etc., is performed based on the assumption that the positional relationship between the fiducial mark plate and the mobile mirrors does not change. However, because of the recent miniaturization of the device pattern, a higher accuracy is required for alignment. If the positional relationship between the fiducial mark plate and the mobile mirror changes due to a small change in temperature of the wafer stage caused by radiation heat, etc., for the exposing light, alignment error exceeding the tolerance may occur.
Suppose that the mobile mirror and the fiducial mark plate are supported by a ceramic member of low expansion coefficient and the fiducial mark plate is made of quartz, The linear expansion coefficient of ceramic and quartz is about 0.5-1.0 ppm /xc2x0 C. Then, if the baseline length for the alignment sensor is about 60 mm and the change in temperature of the wafer stage is about 0.2xc2x0 C., the distance between the mobile mirror and the fiducial mark plate changes by about 6 to 12 nm, and at the same time, the angle between the mobile mirror and the fiducial mark plate may change. Recently, even this much deviation in length and angle may impose a serious hindrance for the alignment accuracy required. For this reason, it is critical that the reticle alignment and the baseline check be conducted with even higher accuracy.
In the above mentioned stage emitting technique, that is, a technique in which a fiducial mark is illuminated from the bottom surface of the fiducial mark plate on the wafer stage, the wafer stage mechanism required for the technique is complex and large sized. The illumination light having the same wavelength as that of the exposing light can be used in the stage emitting technique. However, in the stage emitting technique, the illumination condition such as a numerical aperture and the like is fixed and cannot be changed easily.
Recently, the following techniques are used to improve the resolution of exposure: changing the numerical aperture of the projection optical system; changing the "sgr" value, the coherent factor of the illumination optical system; or using so-called an annular illumination technique, modified illumination technique, or the like. In general, the distortion of the projection image depends on aberration and the telecentric condition of the illumination optical system for exposure. When the techniques described above are used, the image distortion may vary depending on which technique is used. Therefore, the position of the projected image of the reticle pattern (and the reticle alignment mark) on the wafer may change in accordance with the technique used for exposure. This in turn affects the accuracy of the above-mentioned stage emitting technique, degrading the alignment accuracy when these technique are used. Also, the illumination condition in the stage emitting technique cannot easily be matched with the illumination condition for exposure, because it requires a complex, large mechanism.
Accordingly, the present invention is directed to an exposure apparatus that substantially obviates the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a projection exposure apparatus capable of performing highly accurate focused image position measurement.
Another object of the present invention is to provide a projection exposure apparatus capable of performing highly accurate alignment between a mask and a photosensitive substrate.
Another object of the present invention is to provide a projection exposure apparatus capable of performing high speed, highly accurate baseline measurement.
Another object of the present invention is to provide a projection exposure apparatus capable of performing highly accurate alignment between a mask and a photosensitive substrate for various exposure conditions.
A further object of the present invention is to provide a projection exposure apparatus capable of performing high speed, highly accurate baseline measurement for various exposure conditions.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention provides a position detector for use in a projection exposure apparatus to detect a position of a focused image plane at which a focused image of a mask pattern is formed by a radiation flux through a projection optical system having an optical axis, the position detector including a plurality of reference marks disposed in a first direction with predetermined spacings at a position at which the mask pattern is to be placed, the radiation flux illuminating the plurality of reference marks, and thereafter entering the projection optical system to form images of the plurality of reference marks in the focused image plane, the images being arranged in a second direction substantially perpendicular to the optical axis of the projection optical system, and spacings of the images being determined by the predetermined spacings of reference marks; a radiation receiver having a receiving area movable relative to the images of the reference marks to scan the plurality of images successively, the radiation receiver outputting a reception signal indicating the amount of the radiation flux received at the receiving area, the receiving area being smaller than the spacings separating the images of reference marks adjacent in the first direction; a position detector outputting a position signal indicating the position of the receiving area; and a calculation unit processing the reception signal and the position signal to derive the positions of the images of the reference marks.
In another aspect, the present invention provides a projection exposure apparatus for exposing a pattern on a mask onto a substrate, the projection exposure apparatus including a movable mask stage for holding the mask; an illumination optical system directing an exposing radiation flux toward the mask on the movable mask stage to illuminate a plurality of reference marks formed on the mask, the plurality of reference marks being disposed in a first direction with predetermined spacings; an projection optical system receiving the radiation flux that passes through the reference marks to form images of the plurality of reference marks in a focused image plane of the projection optical system, the images being arranged in a second direction substantially perpendicular to an optical axis of the projection optical system, and spacings of the images being determined by the predetermined spacings of the reference marks; a movable substrate stage adjacent the focused image plane, the movable substrate stage being movable in a plane substantially perpendicular to the optical axis and in a direction substantially parallel to the optical axis; a plate fixed to the movable substrate, the plate having an aperture smaller than the spacings separating the images of reference marks adjacent in the first direction; a driving unit moving the movable mask stage and the movable substrate stage relative to each other so that the images of the reference marks are scanned by the aperture; a photo detector outputting a reception signal indicating the amount of the radiation flux that passes through the aperture; a position detector outputting a position signal indicating a position of the plate; and a calculation unit processing the reception signal and the position signal to derive the positions of the focused image plane of the projection optical system.
In another aspect, the present invention provides a projection exposure apparatus for transferring a pattern on a mask to a surface of a substrate by an exposing radiation flux, the projection exposure apparatus including a mask stage for holding the mask, the mask including an alignment mark; a substrate stage for holding the substrate; a first fiducial mark on the substrate stage; an illumination optical system directing the exposing radiation flux toward the mask on the mask stage to illuminate the alignment mark on the mask; a projection optical system receiving the radiation flux that passes through the alignment mark to form an image of the alignment mark; a radiation receiver on the substrate stage, the radiation receiver outputting a reception signal indicating the amount of the radiation flux received at the radiation receiver; a position detector outputting a position signal indicating the position of the radiation reaceiver; an optical system; a mask alignment sensor for receiving from the optical system an image of the first fiducial mark and the image of the alignment mark and in response thereto outputting a mask alignment signal indicating the position of the mask relative to the wafer stage, the optical system being different from the illumination optical system; and a calculation unit processing the reception signal and the position signal and deriving the position of the image of the reference mark relative to the wafer stage, the calculation unit processing the mask alignment signal in accordance with the derived position of the image to calibrate the mask alignment sensor so that the position of the image of the reference mark relative to the wafer stage can be derived from the mask alignment signal generated at the mask alignment sensor.
In another aspect, the present invention provides a position detector for determining a position of a mask relative to a wafer stage in an exposure apparatus for exposing a pattern on the mask onto a wafer on the wafer stage by an exposing radiation flux, the position detector including a first detector optically measuring the position of the mask relative to the wafer stage using a first optical path that is substantially the same as an exposure optical path to be used in exposing the pattern on the mask onto the wafer, the first detector outputting a first position signal indicating the thus measured position of the mask relative to the wafer stage; a second detector optically measuring the position of the mask relative to the wafer stage using a second optical path that is different from the exposure optical path, the second detector outputting a second position signal indicating the thus measured position of the mask relative to the wafer stage; and a controller processing the first position signal and the second position signal to calibrate the second detector so that the position of the mask determined by the first position signal is derived by the second position signal from the second detector.
In another aspect, the present invention provides a method for detecting the position of a focused image plane at which a focused image of a mask pattern on a mask is formed by a radiation flux through a projection optical system in an exposure apparatus, the method including the steps of directing the radiation flux toward the mask to illuminate a plurality of reference marks formed on the mask, the plurality of reference marks being disposed on the mask in a first direction with predetermined spacings; guiding the radiation flux that passes through the reference marks to the projection optical system to form images of the plurality of reference marks in the focused image plane, the images being arranged in a second direction substantially perpendicular to an optical axis of the projection optical system, and spacings of the images being determined by the predetermined spacings of the reference marks; moving a radiation receiving area adjacent the focused image plane relative to the mask to scan the images of the reference marks, the radiation receiving area being smaller than the spacings separating the images of reference marks adjacent in the first direction; outputting a reception signal indicating the amount of the radiation flux received at the radiation receiving area; outputting a position signal indicating a position of the radiation receiving area; and processing the reception signal and the position signal to derive the positions of the images of the reference marks.
In another aspect, the present invention provides a method for calibrating a mask alignment sensor detecting a position of a mask relative to a wafer stage in a projection exposure apparatus for transferring a pattern on the mask onto a wafer on the wafer stage by an exposing radiation flux through a projection optical system, the method including the steps of directing the exposing radiation flux toward the mask to illuminate an alignment mark formed on the mask; guiding the radiation flux passing through the alignment mark to the projection exposure apparatus to form an image of the alignment mark; moving an aperture on the wafer stage adjacent the image of the alignment mark relative to the mask to scan the image of the alignment mark; outputting a reception signal indicating the amount of the radiation flux that passes through the aperture; outputting a position signal indicating a position of the aperture; processing the reception signal and the position signal to derive a position of the image of the alignment mark relative to the wafer stage; transmitting a light beam from the aperture on the wafer stage; guiding the light beam to the projection optical system to form an image of the aperture adjacent the alignment mark; receiving the light beam passing through the mask to output an alignment signal indicating a position of the mask relative to the wafer stage; and processing the alignment signal in accordance with the derived position of the image of the alignment mark in the step of processing the reception signal to derive a relationship between the alignment signal and the position of the image of the alignment mark relative to the wafer stage.
In another aspect, the present invention provides a position detector for use in a projection exposure apparatus to detect a position of a focused image plane at which a focused image of a mask pattern is formed by a radiation flux through a projection optical system having an optical axis, the position detector including a reference mark including a plurality of line-shaped marks disposed in a first direction at a position at which the mask pattern is to be placed, the radiation flux illuminating the reference marks, and thereafter entering the projection optical system to form an image of the reference mark including images of the line-shaped marks in the focused image plane, the images of the line-shaped marks being disposed in a second direction; a radiation receiver having a receiving area movable relative to the images of the line-shaped marks in a plane substantially perpendicular to the optical axis to scan the images of the line-shaped marks successively, the radiation receiver outputting a reception signal indicating the amount of the radiation flux received at the receiving area, the receiving area being larger than the image of the reference mark in the second direction; a position detector outputting a position signal indicating the position of the receiving area; and a calculation unit processing the reception signal and the position signal to derive the positions of the images of the line-shaped marks.
In another aspect, the present invention provides a method for detecting the position of a focused image plane at which a focused image of a mask pattern on a mask is formed by a radiation flux through a projection optical system having an optical axis in an exposure apparatus, the method including the steps of directing the radiation flux toward the mask to illuminate a reference mark formed on a mask, the reference mark including a plurality of line-shaped marks disposed on the mask in a first direction; guiding the radiation flux that passes through the reference mark to the projection optical system to form an image of the reference mark including images of the line-shaped marks in the focused image plane, the images of the line-shaped marks being arranged in a second direction; moving a radiation receiving area relative to the images of the line-shaped marks in the focused image plane to scan the images of the line-shaped marks, the radiation receiving area being larger than the image of the reference mark in the second direction; outputting a reception signal indicating the amount of the radiation flux received at the radiation receiving area; outputting a position signal indicating a position of the radiation receiving area; and processing the reception signal and the position signal to derive the positions of the images of the line-shaped marks.
In another aspect, the present invention provides a method for calibrating a sensor detecting an image of an alignment mark formed on a mask, the method including the steps ofdirecting a first radiation flux toward the mask; outputting a first signal indicating the first radiation flux that passes through the alignment mark; guiding a second radiation flux passing through a projection optical system to the mask, the projection optical system transforming a pattern on the mask to a substrate; outputting a second signal indicating the second radiation flux that passes through the alignment mark; and obtaining an alignment offset based on said first signal and said second signal.
In another aspect, the projection exposure apparatus of the present invention includes an illumination optical system which illuminates a mask printed with alignment marks and a pattern to be transferred; a projection optical system, which projects the pattern image of the mask to be transferred onto the photosensitive substrate; and a wafer stage, which shifts the photosensitive substrate; wherein the wafer stage is formed with first fiducial marks, and second transparent fiducial marks; alignment sensors on the mask side are arranged above the mask (12) to detect the positional deviation of the first or the second fiducial mark on the wafer stage from the alignment marks on the mask via the projection optical system under illumination light having the same wavelength as that of exposing light; and spatial sensors are formed to detect the projected image of the alignment mark on the mask via a projection optical condition via the second fiducial marks under illumination light of the same wavelength and illumination conditions of those of exposure light.
According to the present invention, when aligning the mask, the alignment sensors on the mask side detect the positional deviation of the alignment marks on the mask from the corresponding first fiducial marks using illumination light of the same wavelength as that of exposing light in the downward illumination technique. However, this may cause alignment errors when the illumination condition changes. Therefore, under the same illumination condition as the real exposing light which is actually used, the relative positions of the alignment marks on the mask and the second fiducial mark are detected in advance by both the spatial image sensor and the alignment sensors on the mask side to store the data on the positional deviation between the two relative positions as an offset. By correcting the positional deviation, which is detected by the alignment sensors during the mask alignment, a highly accurate mask alignment (reticle alignment) is performed.
In another aspect, the projection exposure apparatus of the present invention is provided with a calculation unit, which calculates the first relative positional deviation of the mask from the wafer stage, based on the detected signal data obtained by the spatial image sensor during relative-scanning of the projected images of the alignment marks on the mask and the second fiducial mark, and also calculates the second positional deviation of the mask from the wafer stage based on the positional deviation of the alignment marks form the projected image of the second fiducial marks. In addition, the calculation unit provides the offset between the second and the first relative positional deviations; the positional deviation of the alignment mark on the mask, which is detected by the alignment sensors on the mask side, from the projected image of the first fiducial marks is corrected using the offset obtained by the calculation unit.
In the present invention, a photoelectric sensor of the light intensity detection type or the like may be used for the spatial image sensor; the second fiducial marks are used for an apparatus; and image processing is used for the alignment sensor for the mask. In this configuration, by performing a relative scanning for the spatial image sensor and by performing a image sampling in the still state mode of the alignment sensors, the second fiducial marks can be used by other sensors at the same time.
In a further aspect, in the projection exposure apparatus of the present invention, the first or second projection apparatus is provided with an alignment sensor on the substrate side to detect the alignment mark positions on the photosensitive substrate, wherein third fiducial marks are formed in advance in a predetermined positional relationship with respect to the first fiducial marks; wherein the positional deviation of the alignment marks on the mask from the projected images of the first fiducial marks is detected by the alignment sensors on the mask side, and at the same time, the positions of the third fiducial marks are detected by the alignment sensor on the substrate side to measure the relative distance (base line length) between the detection center of the alignment sensor on the substrate side and the center of the image projected onto the wafer stage.
In this case, by correcting the pitch between the first fiducial marks and the pitch between the third fiducial marks, which are measured in advance, using the positional deviation detected by the alignment sensors on the mask side and the positional deviation detected by the alignment sensor on the substrate side, the base line length of the alignment sensor can be obtained. Moreover, in the present invention, by correcting the detection results of the alignment sensors on the mask side via the second fiducial marks, a highly accurate base line length can be obtained even when the illumination condition for exposing light is changed. Moreover, when measuring the positions for the wafer stage using a laser interferometer, a mobile mirror is attached onto the wafer stage. In this case, it is preferable that the member, on which the first and the second fiducial mark are provided, is made of a material having a small thermal expansion coefficient, is formed integral with the mobile mirror. By doing so, the unfavorable effects of thermal deformation from the irradiation heat of exposing light and the like can be reduced.
Also, in the present invention described above, exposing light can be used as illumination light for the alignment sensors and its spatial image sensor; and move-away apparatus can be attached such that the alignment sensors on the mask side are moved away from the optical path of exposing light. In this case, by moving the alignment sensors away from the optical path of the exposing light via the move-away apparatus when using the spatial image sensor, and by moving the alignment sensors back to the optical path of the exposing light, the illumination optical system for exposing light can be commonly used.
Also, according to the coefficient of reflection of the mask, the first and second fiducial mark positions may be adjusted when detecting the positional deviation of the first or the second fiducial mark on the mask from the alignment mark on the wafer stage using the alignment sensors via the projection optical system. For example, when the image processing technique is used for the alignment sensors the position of the first or second fiducial mark can be adjusted to have the image having the maximum contrast which corresponds to the coefficient of reflection of the mask. This provides highly accurate mask alignment and the like even if a low reflective reticle, for example, is used.
It is preferable that the second transparent fiducial marks are formed of a plurality of transparent marks (apertures). This, in turn, means to multiply the second fiducial marks; the positional deviation obtained for each of the transparent marks may be averaged. This provides a highly accurate detection of positional deviation which results in highly accurate mask alignment, etc.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.